A number of chemicals of interest are being tested for mutagenicity and recombinogenicity in Saccharomyces cerevisia D7. One purpose of the study is to evaluate substances which are genetically active in yeast but not in Salmonella. Another, is to compare the activity of yeast with Salmonella for chemicals which are known to be active in Salmonella. Among the chemicals which will be studied are procarbazine (mutagenic in yeast but not in Salmonella), Benzo(a)pyrene, and 2-aminoanthacene.